In known data delivery systems, the delivery apparatus divides the contents data to be delivered into blocks of a predetermined size and transmits the contents data to a communication terminal on a block by block basis as the block is used as unit of data. Then, the communication terminal sequentially receives the units of data transmitted from the delivery apparatus and stores the block IDs annexed to the received units of data.
If the communication between the delivery apparatus and the communication terminal is disabled and the delivery of the contents data is interrupted before all the contents data are transmitted from the delivery apparatus, the communication terminal notifies the delivery apparatus of the block IDs of the units of data it has already received when the communicable state is restored. Then, the delivery apparatus identifies the blocks that have already been delivered and the blocks that have to be delivered to the communication terminal according to the block ID notified from the communication terminal. Thus, the delivery apparatus transmits the units of data of the blocks identified as those that have to be delivered. With this arrangement, the delivery apparatus reliably can transmit the part of the contents data that the communication terminal has not received due to the interruption of delivery, minimizing duplication of transmission of units of data (see, for example, Patent Document 1).
Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. 2002-135350 (page 1, FIG. 1, FIG. 8)
With this arrangement of a data delivery system, there arises occasions where the delivery apparatus provides the communication terminal with contents data along with information on the attributes of contents necessary for altering the attributes relating to reproduction of the contents data.
In such a case, the communication terminal cannot reproduce the contents data if it receives them until it acquires information on the attributes of the contents because it has to reproduce the contents data according to the information on the attributes of the contents. Therefore, the communication terminal receives the contents data along with the information on the attributes of the contents from the delivery apparatus in response to the request for acquiring the contents data.
Now, if the communication terminal has acquired the contents data at the time when the request for acquiring the contents data is made, it receives both the contents data and the information on the attributes of the contents in duplicate for nothing. When the communication terminal receives the contents data in duplicate, it takes a long time for the process of acquiring the contents data and the information on the attribute of the contents (to be referred to as acquisition processing time hereinafter) for nothing to reduce the efficiency of the acquisition process.